As described in the above-referenced '677 application, a variety of communication systems, particularly those installed in mobile (e.g., land-based) platforms, are designed to be environmentally robust in terms of their hardware and signaling format. As a non-limiting example, for the case of a vehicle-mounted, communication system intended for use with a plurality of UHF line-of-sight and satellite links, a multi-link transceiver mounting rack may contain a plurality of diverse pieces of communication equipment, that typically include RF transmitter modules, RF receiver modules, and various digital signal processing modules, which control the operation of the RF components, and interface digital communications signals with attendant encryption and decryption processing circuits. Since each communication link has its own dedicated signalling scheme (modulation format, link protocol, band occupancy assignment, etc.), suppliers of such equipment will typically provide each system as an integrated unit.
One of the standard bus architectures employed for such systems is the VME bus, which is comprised of a pair of multiple lead bus links. One of these bus links has a predefined set of bus connection definitions, to which each module that may be plugged into the VME bus must conform. On the other hand, other than limited power rail assignments, the second bus link has unspecified bus connection definitions, allowing the user to customize the second bus link, or connector interconnects to that bus link, as desired.
Typically, RF signaling circuits and digital signaling modules plug into their own connector slots on the VME bus, in order to provide noise/cross-talk isolation between the RF and digital signal processing components of a given communication system architecture, and to conform with the relatively tight (center-to-center) dimensional spacings between connector slots on the VME bus. Signal connections between modules may be effected by cabling links between the modules and/or use one or more pins of module connectors for the second bus link portion of the VME bus, connection definitions for which would otherwise be unspecified for user customization.
Because VME-based communication system platforms can be expected to be employed in relatively harsh environments that expose the platforms to vibration, foreign matter and potentially damaging temperature variations, VME bus specifications mandate ruggedized housing architectures, that also cool the circuit components and effectively seal them from the external ambient. To accomplish these objectives it has been conventional practice to use very complex (and expensive) chassis-integrated heat transfer structures, on the one hand, and to use more thermally robust circuit components, per se, which undesirably add substantial bulk (and cost) to each circuit board, and thus to the overall housing assembly.
Advantageously, the printed circuit card support and cooling architecture described in the above-referenced '677 application, and diagrammatically illustrated in FIG. 1, is configured to remedy such shortcomings of conventional (VME) bus-mounted communication signal processing module configurations, by reducing the heat resistance paths to within a thermal parameter window that allows the use of commercial grade printed circuit card components. Moreover, its housing architecture has a smaller size than a conventional thermally controlled VME bus-based communication system architecture, so as to facilitate installation of a VME bus-based signal processing system configuration in a relatively limited volume hardware platform.
In particular, the housing structure of the '677 application has a generally regular rectangular, metallic chassis 10 formed of first and second parallel sidewalls 11 and 13, that adjoin parallel end walls 15 and 17, that are generally orthogonal to the sidewalls, and define therebetween a generally rectangular card-insertion cavity 21. The bottom of the chassis 10 is closed by a bottom cover 23, while the top is closed by a top cover 25.
The card insertion cavity 21 is bounded by a pair of slotted frames 27, which contain generally vertical, card-guide slots 29, that are sized to receive guide posts 31 mounted to opposite side edges 33 and 35 of respective printed circuit cards 40. At the bottom of the slotted frames 27 is a connector retention plate 37, supporting a parallel arrangement of spaced-apart, multi-pin electrical connectors 41. The multi-pin connectors receive associated dual in-line multi-pin connectors 43 attached to bottom edges 45 of the circuit cards 40, so that when installed in the chassis, the circuit cards are securely retained in mutually adjacent, spatially parallel relationship.
As shown in greater detail in the exploded views of FIGS. 2 and 3, and in the top view of FIG. 4 and the front view of FIG. 5, in order to cool a respective circuit card 40, a generally frame-configured, thermally conductive (e.g., metallic), convection-based heat exchanger 50 is mounted to one side 53 of the card, and functions to draw heat away from circuit components 42 on a second side 55 of the card. Affixing the heat exchanger 50 directly to the printed circuit card also increases the flexure stiffness of the card; mounting the circuit components 42 and heat exchanger 50 on opposite sides of the card 40 isolates the circuit components from the heat exchanger, preventing the circuit components from being exposed to any potentially corrosive foreign matter that may be present in the cooling fluid (typically external ambient air) flowing through the card's on-board heat exchanger.
The heat exchanger 50 has the general configuration of a frame 60 that a top wall 61, sidewalls 63 and 65, a bottom wall 67, and a back wall 68. These walls of a generally rectangular heat exchanger frame 60 form a cooling fluid flow chamber 70, containing adjacent, generally rectangular cooling fluid flow chamber sections 71 and 73, which are ported by cooling fluid inlet and exhaust ports 81 and 83 formed within the frame's top wall 61. The heat exchanger frame 60 also has a center wall 69, that extends from the top wall 61 to a location 75 spaced apart from the bottom wall 67, so as to form an intra chamber fluid communication port 85 connecting fluid flow chamber sections 71 and 73. A cover plate 80 is secured to the walls of the frame and thereby forms a front wall for the heat exchanger. The heat exchanger frame 60 and its adjoining cover plate 80 are sized to conform with the printed circuit card 40, so that when the cover plate 80 is surface-joined with the first side 53 of the circuit card 40, the entirety of the card surface area upon which the card's circuit components 42 are mounted is thermally coupled to the heat exchanger 50.
This direct face-to-face thermal coupling between the entirety of the first side 53 of the circuit card 40 with cover plate 80 reduces the length of the thermal resistance path between any circuit component 42 and the heat exchanger 50. It also causes the average temperature at any point on the printed circuit card 40 to be uniformly the same, resulting in the lowest possible component temperatures for any given material set and cooling fluid conditions. As a consequence, circuit components 42 mounted to the second side 55 of printed circuit card 40 need not be mil-spec; instead, commercial grade circuit elements, which are considerably less costly, may be used.
The circuit card's on-board heat exchanger 50 further includes first and second thermally conductive, fin-shaped corrugated heat exchanger elements 91 and 93 retained in respective chamber sections 71 and 73 of the cooling fluid flow chamber 70. These fin-shaped corrugated heat exchanger elements 91 and 93 are sized to substantially fill chambers 71 and 73, but leave a fluid circulation region 79 between bottom edges 92 and 94 of elements 91 and 93, respectively, and the bottom wall 67 of the frame 60. This fluid circulation region 79 serves as a return path for cooling fluid that has entered the chamber 71 via inlet port 81 and has traveled (downwardly, as shown at arrows 96) through heat exchanger element 91.
Upon exiting the bottom of heat exchanger element 91 in chamber 71, the cooling fluid then travels through the intra chamber fluid communication port 85 of region 79 and enters the bottom of heat exchanger element 93 in chamber 73. The cooling fluid then travels (upwardly as shown by arrows 98) through heat exchanger element 93 and exits chamber 73 through cooling fluid exhaust port 83. Advantageously, since each cooling fluid port 81 and 83 is located in a plane (top wall 61) that is parallel to the circuit card 40, the effective thickness of the integrated heat exchanger--printed circuit board architecture of the '677 application is such as to allow the circuit card to be readily inserted into any of the connectors 41 of the chassis 10.
In order to supply and remove cooling fluid via the ports 81 and 83, a cooling fluid supply/exhaust plenum 100 is mounted to a top portion 12 of the chassis 10. The plenum 100 includes a cooling fluid supply chamber 101 and a cooling fluid removal chamber 103 that are in fluid communication with the chambers 71 and 73 of the thermally conductive heat exchangers 50 of respective ones of printed circuit cards 40. The plenum 100 includes a generally rectangular frame 110 defined by a first sidewall 111, an end wall 113, a second sidewall 115, and a bottom wall 117, that generally enclose the pair of adjacent, generally rectangular chambers 101 and 103. Chamber 101 serves as a cooling fluid supply chamber and has a cooling fluid supply port 121 formed in a cover 120 that is attached to the top edges of the walls of frame 110. Complementarily, chamber 103 serves as a cooling fluid removal chamber and has a cooling fluid removal port 123 defined by a plenum opening 114 along a side portion 118 of the frame 110 coincident with an opening in the chassis 10.
The plenum frame 110 has a center wall 119 that extends from the first sidewall 111 to the second sidewall 115, so as to isolate the plenum chambers 101 and 103 from each other. Within the plenum chamber 101, the bottom wall 118 has a first set of generally elongated slots 131. Slots 131 are coincident with and adjoin the fluid inlet ports 81 of respective heat exchangers 50 of the circuit cards 40, when the cards are retained in their associated chassis guide slots. The floor portion of the plenum chamber 103 also has a second set of generally elongated slots 133, coincident with and adjoining the fluid exhaust ports 83 of the respective heat exchangers 50, when the cards are retained in their guide slots.
To seal the cooling fluid interfaces between slots 131 and 133 of plenum 100 and the fluid inlet and exhaust ports 81 and 83 of the heat exchangers 50, a multi-slotted gasket 140 is installed between the floor 118 of the plenum 100 and the top walls 61 of the heat exchanger frames 60. The gasket 140 has sets of generally elongated slots 141 and 143, that are coincident with and adjoin the elongated slots 131 and 133 of the plenum 110, and thereby the respective fluid inlet and exhaust ports 81 and 83 of the heat exchangers 50. What results is a cooling fluid path that is convectively coupled with each printed circuit card, yet is sealed off from their components, so that contaminants, which might be present in the cooling fluid (e.g., ambient air drawn in from the outside of the chassis), cannot come in contact with the circuit components of the printed circuit cards.
Now although the improved printed circuit card-mounted heat exchanger architecture described in the above-referenced '677 application is configured to convectively cool the components of the printed circuit cards using the outside ambient, while at the same time sealing the cooled components from the ambient medium, per se, there are circumstances where it is desired to employ standard VME circuit cards (which are cooled by thermally conducting paths interfacing the sides of the cards) in the same housing. Thus, there is a need for a housing configuration which will accommodate and cool both types of circuit cards--those that use less restrictive tolerance (e.g., non mil spec.) components, and those employing mil. spec. tolerance components.